A known variable valve timing control unit which controls an intake timing of an intake valve of an internal combustion engine and an exhaust timing of an exhaust valve of the internal combustion engine independently from each other is disclosed in JP2004-245074A (which will be referred to as Patent reference 1). The known variable valve timing control unit disclosed in Patent reference 1 includes variable valve timing control apparatuses (corresponding to variable valve apparatuses of Patent reference 1) provided at an intake camshaft and an exhaust cam shaft, respectively. The known variable valve timing control unit includes a first control valve hydraulically controlling a phase of each of the variable valve timing control apparatuses and a second control valve hydraulically releasing a lock pin of a lock mechanism (which corresponds to a lock pin mechanism of Patent reference 1) of each of the variable valve timing control apparatuses.
That is, according to Patent reference 1, two of the first control valves are provided for controlling the phase of the variable valve timing control apparatus at an intake side and the phase of the variable valve timing control apparatus at an exhaust side, respectively. In addition, two of the second control valves are provided for releasing the lock of the lock mechanism of the variable valve timing control apparatus at the intake side and the lock of the lock mechanism of the variable valve timing control apparatus at the exhaust side, respectively.
Another known variable valve timing control unit which controls the intake timing of the intake valve of the internal combustion engine and the exhaust timing of the exhaust valve of the internal combustion engine independently from each other is disclosed in JP2006-170024A (which will be referred to as Patent reference 2). The known variable valve timing control unit disclosed in Patent reference 2 includes variable valve timing control apparatuses provided at an intake camshaft and an exhaust cam shaft, respectively. The known variable valve timing control unit includes control valves each of which hydraulically controls a phase of the corresponding variable valve timing control apparatus and hydraulically controls a lock pin of a lock mechanism of the corresponding variable valve timing control apparatus.
The known variable valve timing control unit disclosed in Patent reference 2 includes the two control valves for the two variable valve timing control apparatuses, respectively. Each of the control valves includes functions of controlling the phase and controlling the lock mechanism, corresponding to an operation position of a spool of the control valve.
According to each of Patent references 1 and 2, an opening/closing timing of an intake valve and an opening/closing timing of an exhaust valve are changed reflecting a rotational speed of an internal combustion engine and/or temperatures of the internal combustion engine, for example. As a result, a fuel-efficient operation is achieved.
However, in Patent reference 1, the two control valves for the phase control and the two control valves for the lock control are provided corresponding to the two variable valve control apparatuses. That is, the four valves are needed in total, which leads to an increase in the number of parts and an increase in size of the system.
In addition, Patent reference 2 includes the two control valves for the respective two variable valve timing control apparatuses, and each of the control valves includes the functions of the phase control and the lock mechanism control. According to Patent reference 2, the number of the parts is reduced, however, each of the control valves includes a complicated configuration and is increased in size.
A need thus exists for a variable valve timing control unit which is not susceptible to the drawback mentioned above.